Fire detector



April 17, 1945. N. J. SMITH 2,373,856

FIRE DETECTOR Filed Dec. 31, 1943 5 Sheets-Sheet 3 Patented Apr. 17, 1945 FIRE DETECTOR Norman J. Smith, Medfield, Masa, assignor to Fenwal Incorporated, Ashland, Mass, a corporation of Massachusetts Application December 31, 1943, Serial No. 516,602

6 Claims.

This invention relates to fire detectors, and more especially to such detectors of the gas thermometer type wherein agas filled detector tube extends around the space to be protected.

The object of the invention is to provide a fire detector of this type which is particularly adaptable for installation on airplanes, or for use in other relations where the detector is subject to violent variations both in barometric pressure and the temperature of the air surrounding the detector.

A fire detector of the gas thermometer type comprises a diaphragm actuating gas filled element carrying a contact member era-operating with a second contact member for closing an indicating or alarm circuit when the gas pressure in said element is increased due to an abnormal rise in temperature .caused by a fire in the vicinity of the detector tube. However, a substantial change in the temperature of the ambient air would vary the pressure in the gas filled element suificiently either to close the gap between the contact members, unless such gap were so long as to render the detector insensitive, or else to increase the length thereof and thereby render the detector insensitive; while a substantial variation in barometric pressure would vary the separation of the contact members in such manner as to change the original setting of the apparatus and render the device ineflective.

It is therefore the object of the present invention to provide means whereby the gap between the contact members is rendered independent of changes in barometric pressure and in the temperature of the ambient air, in order that a relatively short gap may be maintained of constant length under all conditions, thereby maintaining the sensitivity of the detector and preventing false alarms due to the excessive changes both in barometric pressure and temperature when the plane carrying the alarm device is flying at high altitudes where both the barometric pressure and the ambient temperature are extremely low.

These objects are attained by providing a floating support for one of the contact members, the position of which depends upon barometric pressure and the temperature of the ambient air.

In the accompanying drawings,

Figure 1 is a plan view oi an alarm system embodying my invention.

Fig. 2 is a central vertical section taken on the line 1-2 of Fig. i.

Fig. 3 is a plan view of a modification.

Fig. 4 is a vertical section taken on the line 4-4 of Fig. 3.

Figs. 5 and 6 are diagrammatic representations of further modifications, and

Fig. '7 is a schematic view, hereinafter referred to in explaining the mode of operation of all the embodiments of the invention.

In the particular drawings selected for more fully disclosing the principle of operation of my invention. ll is a base member provided with a chamber ii closed by a resilient diaphragm l2 on which is mounted a circuit making and breaking contact member l3.

Rising from the base is a post It provided with a shoulder supporting a washer I5 above which is placed a tension spring l-i.

Oppositely disposed to said post is a spring post it supporting at its upper end a plate Ill integral with a disc i0" which is provided with a chamber i8 closed by a diaphragm i9. By means of the adjusting screw 20 acting on the extension W of said disc, the relative position of the members ill and it provided with the chambers il, l8, may be slightly adjusted.

A rectangular yoke 2i is secured in any appropriate manner to the upper face of the diaphragm l9. To the lower element 22 of said yoke, secured to the upper part thereof by the side members 23, 23, is a circuit making and breaking contact member 24 arranged for co-operation with the contact member l3. The detector tube 26, which extends around the space to be protected, communicates with the chamber H by the port 21, and a capillary tube 28 is connected between the chambers ii and It. By any suitable means, the chambers and detector tube may be filled with a fluid, such as air, or a volatile liquid under pressure.

In Fig. 4 is indicated a duct 28 controlled by a valve 29, whereby such fluid pressure may be impressed upon the chambers and detector tube.

It will be noted that the contact members are arranged for unison action by the pressure responsive devices by which they are actuated, that is, for simultaneous movement in the same direction at uniform rates of speed. The casing 30 that may be used for enclosing the fire detector is not air-tight and therefore changes in barometric pressure will cause the diaphragms and the contact members associated therewith to move in unison, thereby maintaining constant the length of the gap between the contact members, provided, however, that the ambient temperature remains constant. However, the excessive changes in ambient temperature experienced by a the detector of this type carried by an airplane requires not only automatic barometric correction to prevent false alarms but also an automatic temperature reset, and such reset is afforded by the capillary tube connection between said chambers.

The ambient temperature changes are, of course, relatively slow compared to the changes in the temperature of the gas in the detector tube and chambers caused by a fire in the neighborhood of the detector tube. As the chambers are connected by a capillary tube, or other suitable choking connection, the relatively slow changes in pressure caused by the changes in ambient temperature will permit the diaphragms to move in unison, thereby maintaining constant the length of the relatively short gap between the contact members, but a quick rise in the pressure created by a fire in the vicinity of the detector tube, will raise the diaphragm I2 instantly, thereby closing the indicator circuit, because such sudden change in pressure will not be efiective to raise the diaphragm I9 and the contact member carried thereby until a considerable time after the circuit has been closed.

A typical indicator circuit is indicated at and includes an indicator, such as a red light 4|, both contact members I3 and 24, and a source of electrical energy 42. One terminal of the circuit is connected to the upper contact member, as, for example, by connecting it to the yoke carrying said member as shown at 40', and the other in the present instance, is grounded at G, the lower contact member being grounded at G through the base I0 and detector tube 26.

In Fig. 4 is shown means that may be employed for compensating the effect on the gap between the contact members 50, 5I, of inequalities of action of the diaphragms 52, 53. 4

The diaphragm actuating gas filled member 54, a well known article of commerce, is supported in a chamber formed in the base and a similar element 56 is disposed in a chamber formed in the disc 57 carried by the post 58 and secured thereto by the screw 59. The capillary tube 60 affords communication between the two gas filled chambers by way of passages formed in the base and in the elements 54, 56. The operation of the detector is the same as that described above in connection with Fig. 2.

As it is difficult to secure a pair of exactly matched diaphrgams, adjustments are provided I as follows:

The vertical side 6| ofa yoke is provided with a hinge member 62 which may be electrically Welded to said vertical side and a pintle 63 passes through said hinge member and a pair of oppositely disposed lugs 64 integral with the disc 51. The forward end of the upper horizontal member 65 of the yoke is resiliently attached by the spring 56 to the bracket 61, which is secured to the disc 51 by the screw 59. Embracing the upper yoke member 65 is a slide I0 movable longitudinally of said yoke member by the screw 1|, which passes through the block 12 secured to and extending transversely from said member 65. The underside/of the slide is provided with a finger I0 disposed to contact the upper face of the diaphragm 53. As diaphragms of this nature generally are corrugated, I prefer to interpose between the diaphragm and finger a thin resilient strip I3 secured in any suitable manner by its flange 14 to the disc 51.

The lower horizontal member I5 of said yoke supports the contact member SI and the relative position of the two contact members may be through the vertical side 01' the yoke and is in threaded engagement with the block 11 secured to and projecting upwardly from said member 16.

The finger 10' being held resiliently against the upper diaphragm 53 or the resilient strip resting thereon, will, in accordance with its position, magnify or diminish the movement of said diaphragm, thereby compensating for any inequalities in spring rating of the two diaphragms and securing unison movement thereof and of the contact members carried thereby. An initial gap adjustment may be obtained by the screw I6. Thus, it Will be seen that the screw actuated finger 10' provides a means for adjusting the rate of movement of one diaphragm with respect to that of the other for a given change in temperature after the screw 76 has determined the initial length of the gap between the co-operating contact members.

In Figs. 2 and 4, thediaphragms are spaced axially, while in Figs. 5 and 6, they are spaced with their axes parallel. In Fig. 5, the diaphragm 80 carries on end of an arm 8| to the other end of which is attached the contact member 82 disposed for co-operation with the 'contact member 83 which is secured to the upper face of the diaphragm 84. The capillary tube 85 is connected between the chambers 86, 81, which are closed by the diaphragms 80, 84, respectively.

In Fig. 6, a lever arm fulcrumed at 9| carries the contact member 92 disposed for co-operation with the contact member 93 secured to the diaphragm 94 which closes the chamber 95. The slide 96 embracing said lever is provided with a finger 91 disposed to contact the diaphragm 98 closing the chamber 99 or else a flat strip such as the strip 13 hereinbefore described in connection with Fig. 4.

The arrangement shown in Fig. 5 will be employed with matched diaphragms and that of Fig. 6 with diaphragms wherein there is inequality of action.

' In Fig. 7, I have shown a normally open supervisory circuit for testing the maintenance of fluid pressure in the detector, said circuit consisting in the present instance of a heating element I00 surrounding, or else arranged in proximity to the detector tube, one end of which element is grounded at G through the detector tube and the other connected to the manually operated switch IOI, an indicator such as a green light I02 and a battery or other suitable source of electrical energy 42. By closing the switch and thereby raising the temperature of the gas in the detector tube, the green lamp I02 will be lighted if the heating element is in working order, and in such case, the red lamp 4I also will be lighted if the fluid pressure in the tube and chambers has not been reduced below that required to give satisfactory operation.

The system is provided also with a normally closed supervisory circuit, comprising any suitable switch means, such as the resilient strip I03 carried by the diaphragm I2 and normally maintained against the contact point I04 connected to the green lamp I05 and battery 42, When the pressure in the system is reduced below a prevaried, if necessary, by the screw 16 which passes 75 determined value, the circuit will be opened automatically between the contact members I03, I04. It will be noted that both supervisory circuits and the indicator circuit have a common source of voltage.

Having thus described illustrative embodiments of my invention without, however, limiting the same, thereto, what I claim and desire to secure by Letters Patent is:

1. A fire detector comprising in combination, two spaced chambers, diaphragms closing the respective chambers, co-operating circuit making and breaking contact members, each disposed for actuation by one of said diaphragms, detector tubing communicating with one of said chambers and extending around the space to be protected, and a capillary tube connecting said chambers, said tube and chambers being filled with a fluid under pressure.

2. A fire detector comprising in combination, two spaced chambers, diaphragms closing the respective chambers, co-operating circuit making and breaking contact members, each carried by one of said diaphragms, detector tubing communicating with one of said chambers and extending around the space to be protected, and a capillary tube connecting said chambers, said tube and chambers being filled with a fluid under pressure.

3. A fire detector comprising in combination, two spaced chambers, diaphragms closing the respective chambers, co-operating circuit making and breaking contact members, each disposed for actuation by one of said diaphragms, detector tubing communicating with one of said chambers and extending around the space to be protected,

a capillary tube connecting said chambers, said tube and chambers being filled with a fluid under pressure, and means to;- compensating the effeet on the gap between said contact members of inequalities of action of said diaphragms.

4. A fire detector comprising in combination, two spaced chambers, diaphragms closing the repective chambers, co-operating circuit making and breaking contact members, each disposed for actuation by one or said diaphragm, detector tubing communicating with one of said chambers and extending around the space to be protected, a capillary tub connecting said chambers, said tube and chambers being filled with a fluid under pressure, and means for adjusting the rate of movement of one of said diaphragms with respect to that of the other for a given change in temperature.

5. A fire detector comprising in combination, two spaced chambers, diaphragms closing the respective chambers, co-operating circuit making and breaking contact members, each disposed for actuation by one of said diaphragms, detector tubing communicating with one of said chambers and extending around the space to be protected, a capillary tube connecting said chambers, said tube and chambers being filled with a fluid under pressure, and means for setting the initial length of the gap between said contact members.

6. A fire detector comprising in combination, a pressure responsive element, a circuit making and breaking contact member disposed for actuation by said pressure responsive element, a second pressure responsive element, a second circuit making and breaking contact member disposed for actuation by said second pressure responsive element and arranged for co-operation with the contact member first named, said second pressure responsive element being constructed and arranged to constitute a floating support for said second contact member, and means subjecting said pressure responsive elements to the same source of gas under pressure, whereby the length of the gap between said contact members is maintained constant and rendered independent of changes in atmospheric temperature and pressure.

NORMAN J. SMITH. 

